The present invention relates to a high-alumina ceramic composition having a small dielectric loss in the high frequency range.
Conventional waveguides used with electronic circuits designed to operate with millimeter waves in the high frequency range (.gtoreq.30 GHz) are typically made of metals. Recently, titanates such as barium titanate, strontium titanate, and calcium titanate, as well as alumina ceramics have been considered as promising alternatives to metals as the material for waveguides operating with millimeter waves. However, titanates have a dielectric loss tangent (tan .delta.) of the order of 10.sup.-4 and are too high in dielectric loss to make the titanates suitable for operation with millimeter waves. Alumina ceramics having a satisfactory low tan .delta. are very difficult to produce on a commercial scale, and hence are not suitable for use in practical applications.